Preparation and characterization of pore-wall modification gradients generated on porous silicon photonic crystals using diazonium salts

One-dimensional photonic crystals (rugate filters) constructed from porous silicon were modified by the chemical hydrosilylation of terminal alkenes (decyl, 10-carboxydecyl, and 10-hydroxydecyl) in the presence of a concentration gradient of diazonium salt initiators. The concentration gradient was generated by vertically orienting the Si wafer containing the porous Si layer in an alkene solution and then introducing the diazonium salt at the bottom edge of the wafer. Slow diffusion of the salt led to a varying density of grafted alkene across the surface of the porous layer. The modified surfaces were end-capped with methyl groups by electrochemical grafting to impart improved stability and greater hydrophobicity. The surface modified with 10-carboxydecyl species was ionized by deprotonation of the carboxy groups to increase the hydrophilicity of this porous silicon surface. The pore-wall modification gradients were characterized using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). The more hydrophilic portion of the gradient changes color when water infiltrates the porous nanostructure because of a shift in the stop band of the photonic crystal. The more hydrophobic portion of the gradient excludes water, although mixtures of water and ethanol will infiltrate this region, depending on the concentration of ethanol in the mixture. A simple visual sensor for small quantities of ethanol in water, capable of detecting ethanol concentrations of between 0 and 8% with a resolution of 1% is demonstrated.     

液相渗硅法制备多孔Si/SiC生物形态陶瓷

榉木经高温热解转化为碳模板,通过液相渗硅反应（LSIP）,在1550℃,1.5h渗硅,1700℃排硅制备了保持木材微观结构的多孔Si/SiC陶瓷。利用X-射线衍射分析（XRD）, 扫描电子显微镜（SEM）,压汞技术对样品的物相构成、显微结构和孔径分布进行了分析,利用阿基米德法和三点弯曲法测定了多孔陶瓷的显气孔率、密度和弯曲强度。结果表明,最终产物由主晶相β-SiC和少量的Si组成;控制高温排硅时间可以得到孔隙率为16％~32％的多孔Si/SiC陶瓷,可调控其产物的相组成和力学性能。对LSIP工艺的反应机理进行了探讨。     

Response of nanoparticle-based one-dimensional photonic crystals to ambient vapor pressure

Herein we report an analysis of the variation of the optical properties of different nanoparticle-based one-dimensional photonic crystal architectures versus changes in the ambient vapor pressure. Gradual shift of the optical response provides us with information on the sorption properties of these structures and allow us to measure precise adsorption isotherms of these porous multilayers. The potential of nanoparticle-based one-dimensional photonic crystals as base materials for optical sensing devices is demonstrated in this way.     

Light propagation in triple-film hetero-opals

Spectra of transmitted and forward scattered light of single opal films and triple-film hetero-opals have been compared. The presence of an intermediate film in hetero-opal results in an anomalous increase of the scattered light intensity and in the change of the mainly ballistic light propagation regime to the mainly diffusive one in the frequency range of the photonic bandgap defect state.     

原代大鼠肝细胞在多孔壳聚糖及其复合物支架上的培养

研究了原代肝细胞在壳聚糖及其复合物多孔支架上的生长及代谢.结果表明,细胞在多孔壳聚糖支架上生长良好,且密度、代谢活性较单层培养条件下有大幅度提高,细胞在7d后仍能保持较强的分泌白蛋白和合成尿素的功能,壳聚糖复合物上肝细胞的代谢活性更高.还从材料的化学结构和几何形态角度对这种材料的优势进行了讨论.     

Local heating of discrete droplets using magnetic porous silicon-based photonic crystals

This paper describes a method for local heating of discrete microliter-scale liquid droplets. The droplets are covered with magnetic porous Si microparticles, and heating is achieved by application of an external alternating electromagnetic field. The magnetic porous Si microparticles consist of two layers. The top layer contains a photonic code and it is hydrophobic, with surface-grafted dodecyl moieties. The bottom layer consists of a hydrophilic silicon oxide host layer that is infused with Fe3O4 nanoparticles. The amphiphilic microparticles spontaneously align at the interface of a water droplet immersed in mineral oil, allowing manipulation of the droplets by application of a magnetic field. Application of an oscillating magnetic field (338 kHz, 18 A rms current in a coil surrounding the experiment) generates heat in the superparamagnetic particles that can raise the temperature of the enclosed water droplet to >80 degrees C within 5 min. A simple microfluidics application is demonstrated: combining complementary DNA strands contained in separate droplets and then thermally inducing dehybridization of the conjugate. The complementary oligonucleotides were conjugated with the cyanine dye fluorophores Cy3 and Cy5 to quantify the melting/rebinding reaction by fluorescence resonance energy transfer (FRET). The magnetic porous Si microparticles were prepared as photonic crystals, containing spectral codes that allowed the identification of the droplets by reflectivity spectroscopy. The technique demonstrates the feasibility of tagging, manipulating, and heating small volumes of liquids without the use of conventional microfluidic channel and heating systems.     

Enhancement of the fluorescence intensity of DNA intercalators using nano-imprinted 2-dimensional photonic crystal

We have fabricated polymer-based 2-dimensional photonic crystals that play a key role in enhancing the fluorescence of DNA intercalators. Highly ordered 2-dimensional photonic crystals possessing triangle-shaped and nm-sized hole arrays were fabricated on a 100 μm thick polymer film using nano-imprint lithography. Samples of double-stranded DNAs (sizes: 4361 and 48502 bp; concentration: 1 pM to 10 nM) were adsorbed on the surface of the 2-dimensional photonic crystal by electrostatic interactions and then treated with intercalators. It is found that the fluorescence intensity of the intercalator is enhanced by a factor of up to 10 compared to the enhancement in the absence of the 2-dimensional photonic crystal. Fluorescence intensity increases with increasing length and concentration of the DNAs. If the 2-dimensional photonic crystal is used as a Bragg reflection mirror, the enhancement of fluorescence intensity can be easily observed using a conventional spectrofluorometer. These results suggest that the printed photonic crystal offers a great potential for highly sensitive intercalator-based fluorescent detection of DNAs.

用STM研究电化学阳极氧化制备的多孔硅

本文利用扫描遂道显微镜(STM)并辅以快速富立叶变换(FFT)和数据拟合等数学方法对电化学阳极氧化法制备的多孔硅(PS)的微结构及形貌进行了研究。同时研究了多孔硅的微结构与其发光性质和电化学性质的相互关系。研究表明,在其他条件不变情况下,随阳极氧化电流密度的增大,所形成的多孔硅的微孔向纵深延伸,多孔硅层增厚,微孔相连后形成的硅柱变细,发光强度增大,发光峰位明显蓝移,与单晶硅相比,多孔硅电极的平带电位明显负移,而电极电流在两极区内均增大。     

微载体糖基化修饰及培养基中添加果糖对大鼠原代肝细胞体外培养的影响

采用对大孔壳聚糖微载体进行糖基化修饰和培养基中添加果糖两种方式考察了果糖对原代大鼠肝细胞体外培养的影响。结果显示,肝细胞在果糖修饰大孔微载体上聚集生长,形态良好,保持了较高的白蛋白分泌和尿素合成活性,表明果糖修饰大孔壳聚糖微载体是较理想的细胞培养支架材料。培养基中加入果糖,肝细胞乳酸脱氢酶泄漏明显降低,白蛋白分泌与尿素合成活性进一步提高,显示有利于受损细胞功能的恢复。     

Effect of continuous magnetic field on the growth mechanism of nanoporous anodic alumina films on different substrates

The effects induced by an external homogeneous magnetic field on the oxide film growth on aluminum in aqueous solutions of oxalic and sulfuric acid and on surface morphology of the alumina films were studied. Aluminum films of 100 nm thickness were prepared by thermal evaporation on SiO₂/Si and glass-ceramic substrates. The pore diameter for oxalic acid alumina films on the SiO₂/Si substrate decreased by 0.8 nm, the interpore distance by 5.9 nm, and cell diameter by 6.9 nm if a magnetic field of 0.5 T was applied. When aluminum was anodized in sulfuric acid on the same substrate, the significant changes in parameters of porous structure of alumina, which were similar to the ones in oxalic acid, are firstly observed in stronger magnetic fields (of 0.7 T). On the basis of data obtained in this study and of previous investigation on the negative space charge and thermally activated defects in anodic alumina, we concluded that the intensity of the magnetic field is associated with energy of electron traps and that the changes of cell diameter characterize the trap concentration. The energy of electron traps in oxalic acid alumina films was proved to be smaller than the one in films formed in sulfuric acid, but the concentration of traps was of the same order of magnitude. When the substrate was replaced with the glass-ceramic one, the pore diameter in oxalic acid alumina films increased to ca. 17.6 nm.     

Single-step fabrication and characterization of photonic crystal biosensors with polymer microfluidic channels

A method for simultaneously integrating label-free photonic crystal biosensor technology into microfluidic channels by a single-step replica molding process is presented. By fabricating both the sub-micron features of the photonic crystal sensor structure and the >10 microm features of a flow channel network in one step at room temperature on a plastic substrate, the sensors are automatically self-aligned with the flow channels, and patterns of arbitrary shape may be produced. By measuring changes in the resonant peak reflected wavelength from the photonic crystal structure induced by changes in dielectric permittivity within an evanescent field region near its surface, detection of bulk refractive index changes in the fluid channel or adsorption of biological material to the sensor surface is demonstrated. An imaging detection instrument is used to characterize the spatial distribution of the photonic crystal resonant wavelength, gathering thousands of independent sensor readings within a single fluid channel.     

In situ monitoring of structural changes during colloidal self-assembly

Reflectance spectroscopy is utilized to monitor structural changes during the self-assembly of a monodisperse colloidal system at the meniscus of a sessile drop on an inert substrate. Treating the ordered colloidal structure as a photonic crystal is equivalent to monitoring the changes in the photonic band gap (PBG) as the colloidal system self-assembles heterogeneously into a crystal through solvent evaporation in ambient conditions. Using a modified Bragg's law model of the photonic crystal, we can trace the structural evolution of the self-assembling colloidal system. After a certain induction period, a face-centered cubic (FCC) structure emerges, albeit with a lattice parameter larger than that of a true close-packed structure. This FCC structure is maintained while the lattice parameter shrinks continuously with further increase in the colloidal concentration due to drying. When the structure reaches a lattice parameter 1.09 times the size of that of a true close-packed structure, it undergoes an abrupt decrease in lattice spacing, apparently similar to those reported for lattice-distortive martensitic transformations. This abrupt final lattice shrinkage agrees well with the estimated Debye screening length of the electric double layer of charged colloids and could be the fundamental reason behind the cracking commonly seen in colloidal crystals.     

带隙可调各向同性蛋白石光子晶体的制备与研究

用旋涂法将聚苯乙烯微球组装成光子晶体,研究了此光子晶体的特点,并分析了在单一微球粒径下旋涂参数对光子带隙的影响.结果表明:旋涂法制备的光子晶体具有各向同性特点,其光子带隙由旋涂参数决定.光子晶体的反射波段取决于乳液中微球的质量分数,而反射强度取决于旋涂层数.因此,在设计光子晶体时,可以根据需要,通过微球的质量分数和旋涂...     

Synthesis and Comparative Investigation of Silicon Transition Metal Silicide Composite Anodes for Lithium Ion Batteries

A significant increase in energy density of lithium ion batteries (LIBs) can be achieved by using high‐capacity, silicon (Si)‐based negative electrode materials. Several challenges arise from the enormous volumetric changes of Si during lithiation/delithiation, such as disintegration/pulverization of the active material and the electrode as well as ongoing electrolyte decomposition, leading to rapid capacity fading. Here, we synthesize and comparatively investigate three different porous transition metal‐Si‐carbon composite materials that are composed of an active Si phase and the corresponding inactive metal‐silicide phases. In this material design, the inactive phases, as well as the pores serve as a buffer to attenuate the previously mentioned detrimental effects. The synthesized materials are studied with respect to their structural and surface properties and are characterized electrochemically regarding their rate performance, and long‐term charge/discharge cycling stability. Thereby, the composite materials show a promising rate capability and a high specific capacity. Their low initial Coulombic efficiency, due to the porous structure, can be partially compensated by pre‐lithiation. This is demonstrated by the application of the synthesized materials in a LIB full‐cell set‐up vs. NMC‐111 cathodes, where the amount of lithium is confined due to anode/cathode capacity balancing.     

Optical ammonia gas sensor based on a porous silicon rugate filter coated with polymer-supported dye

An ammonia gas sensor chip was prepared by coating an electrochemically-etched porous Si rugate filter with a chitosan film that is crosslinked by glycidoxypropyltrimethoxysilane (GPTMS). The bromothylmol blue (BTB), a pH indicator, was loaded in the film as ammonia-sensing molecules. White light reflected from the porous Si has a narrow bandwidth spectrum with a peak at 610 nm. Monitoring reflective optical intensity at the peak position allows for direct, real-time observation of changes in the concentration of ammonia gas in air samples. The reflective optical intensity decreased linearly with increasing concentrations of ammonia gas over the range of 0–100 ppm. The lowest detection limit was 0.5 ppm for ammonia gas. At optimum conditions, the full response time of the ammonia gas sensor was less than 15 s. The sensor chip also exhibited a good long-term stability over 1 year. Therefore, the simple sensor design has potential application in miniaturized optical measurement for online ammonia gas detection.     

Submicron scale patterning in sintered silica colloidal crystal films using a focused ion beam

Focused ion beam milling is used to fabricate micron and submicron scale patterns in sintered silica colloidal crystal films. Rectangular cavities with both solid and porous boundaries, fluidic channels, and isolation of a small number of packed spheres are patterned. The ion beam can pattern sintered films of individual submicron size spheres and create patterns that cover up to 40 mum in less than 15 min. The experiments in this work indicate that the amount of redeposited material on the surface of a milled cavity determines whether the surface will be porous or solid. FIB direct patterning has applications in colloidal crystal based lithography, integrated photonic devices, optofluidic devices, and micrototal-analytical systems.     

Exploring the dark side of MTT viability assay of cells cultured onto electrospun PLGA-based composite nanofibrous scaffolding materials

One major method used to evaluate the biocompatibility of porous tissue engineering scaffolding materials is MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The MTT cell viability assay is based on the absorbance of the dissolved MTT formazan crystals formed in living cells, which is proportional to the number of viable cells. Due to the strong dye sorption capability of porous scaffolding materials, we propose that the cell viability determined from the MTT assay is likely to give a false negative result. In this study, we aim to explore the effect of the adsorption of MTT formazan on the accuracy of the viability assay of cells cultured onto porous electrospun poly(lactic-co-glycolic acid) (PLGA) nanofibers, HNTs (halloysite nanotubes)/PLGA, and CNTs (multiwalled carbon nanotubes)/PLGA composite nanofibrous mats. The morphology of electrospun nanofibers and L929 mouse fibroblasts cultured onto the nanofibrous scaffolds were observed using scanning electron microscopy. The viability of cells proliferated for 3 days was evaluated through the MTT assay. In the meantime, the adsorption of MTT formazan onto the same electrospun nanofibers was evaluated and the standard concentration-absorbance curve was obtained in order to quantify the contribution of the adsorbed MTT formazan during the MTT cell viability assay. We show that the PLGA, and the HNTs- or CNTs-doped PLGA nanofibers display appreciable MTT formazan dye sorption, corresponding to 35.6-50.2% deviation from the real cell viability assay data. The better dye sorption capability of the nanofibers leads to further deviation from the real cell viability. Our study gives a general insight into accurate MTT cytotoxicity assessment of various porous tissue engineering scaffolding materials, and may be applicable to other colorimetric assays for analyzing the biological properties of porous scaffolding materials.     

Enhancing plasma peptide MALDI-TOF-MS profiling by mesoporous silica assisted crystallization

Promising profiling techniques based on new material/solid phase extraction for capturing “molecular signatures” from body fluids are being coupled to MALDI-TOF-MS. Sample preparation significantly influences spectrum quality in this ionization method. Mesoporous silica beads (MSB), by the means of nano-sized porous channels with high surface area, enable harvesting of peptides from plasma and serum excluding large size proteins. We have investigated the morphology of a sample slurry, developed as a new tool for plasma peptides enrichment based on mesoporous materials. Our study highlights a correlation between crystals morphology and enhanced performances in MALDI-TOF-MS analysis. This is the first report which correlates the increase in signal intensity with crystal formation in samples preparations which make use of various kinds of slurries for the analysis of samples clinically relevant like human plasma.     

The electro-optical properties of 'charged' PDLCs

The application of high intensity electric fields to polymer dispersed liquid crystal (PDLC) films can induce changes in their electro-optical properties and morphology. In particular, a quasilinear electro-optical response to an external electric field can be achieved if an internal built-in d.c. field is induced. In this work, we show how the liquid crystal/polymer weight ratio influences the electro-optical response of 'charged' PDLCs, i.e. of PDLC films after the application of a high intensity electric field. We observed that a quasilinear electro-optical response can be achieved in a well determined range of composition. Larger liquid crystal concentrations are unable to maintain the built-in field, while PDLCs with lower liquid crystal loadings do not allow the onset of a built-in d.c. field.     

A porous silicon-palladium composite film for optical interferometric sensing of hydrogen

Porous Si Fabry-Pérot films are coated with Pd via immersion plating. The materials are characterized by electron microscopy and infrared spectroscopy. The Pd-coated porous Si samples exhibit distinct Fabry-Pérot fringes in the optical reflection spectrum due to thin film optical interference in the porous Si layer, though the reflectivity spectrum loses fidelity upon Pd coating. The effect of H2 exposure on the interference spectrum is studied. Absorption of hydrogen into Pd induces a lattice expansion, which results in a shift of the optical fringes and a decrease in the reflected intensity. The detection limit measured at room temperature is approximately 0.2% (by volume) in an N2 carrier gas, with a response time of a few seconds.